Intra-articular joint replacement and method

ABSTRACT

Methods of implanting a prosthesis to repair a joint include displacing a first bone from the joint formed by an intersection between the first bone and a second bone. An end portion of the first bone is resected to define a resected end. A concavity is formed into the resected end using a shaping tool. The bone is compacted to form a support layer lining the concavity. The prosthesis is implanted in the concavity against the support layer without attaching the prosthesis to the support layer. The joint is reformed with the prosthesis such that the prosthesis remains unattached to the support layer and the first and second bones articulate about the prosthesis.

BACKGROUND

One type of method used to replace damaged joints (e.g., shoulderjoints) is interpositional arthroplasty. The method of interpositionalarthroplasty uses tissue from the patient or an artificial replacementto repair a damaged or malformed joint. An interpositional implant ispositioned at the joint to act as an engagement surface between twoadjacent bone structures to allow articular movement.

SUMMARY

Some embodiments relate to a method of implanting a prosthesis to repaira joint. The method includes displacing a first bone from the jointformed by an intersection between the first bone and a second bone. Anend portion of the first bone is resected to define a resected end. Aconcavity is formed into the resected end using a shaping tool. The boneis compacted to form a support layer lining the concavity. Theprosthesis is implanted in the concavity against the support layerwithout attaching the prosthesis to the support layer, the prosthesisincluding a first surface and a second surface opposite the firstsurface, each of the first and second surfaces being substantiallyconvex in shape. The joint is reformed with the prosthesis such that theprosthesis remains unattached to the support layer and the first andsecond bones articulate about the prosthesis.

Some embodiments relate to a bone recess forming tool. The tool includesa forming head having a forming surface defining a convex hemisphericalportion and an upswept portion extending beyond the convex hemisphericalportion, the forming surface being adapted to form a recess into a bone.

Still other embodiments relate to a surgical kit of parts for implantingjoint prostheses available in a plurality of graduating diameters. Thekit includes a plurality of test prostheses each graduating in diametersuch that each one of the test prostheses has a diameter correspondingto one of the available graduating diameters of the joint prosthesis.The kit also includes a plurality of reamers each graduating in diametersuch that each one of the reamers has a diameter corresponding to one ofthe available graduating diameters of the joint prosthesis. The kit alsoincludes a plurality of compactors each graduating in diameter such thateach one of the compactors has a diameter corresponding to one of theavailable graduating diameters of the joint prosthesis. Each one of thetest prostheses, reamers, and compactors having the same diameter formsan operational tool set for implanting a joint prosthesis of the samediameter, and further wherein each of the test prostheses, reamers, andcompactors include colored indicia indicating to which operational toolset a particular test prosthetic, reamer, and compactor belongs.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a joint system, according to some embodiments.

FIG. 2 shows an interpositional implant, according to some embodiments.

FIG. 3 shows another interpositional implant, according to someembodiments.

FIG. 4 shows another joint system, according to some embodiments.

FIG. 5 shows a surgical kit, according to some embodiments.

FIG. 6 shows a reamer of the surgical kit of FIG. 5 , according to someembodiments.

FIG. 7 shows a test implant and handle of the surgical kit of FIG. 5 ,according to some embodiments.

FIG. 8 shows a starter compactor of the kit of FIG. 5 , according tosome embodiments.

FIG. 9 shows an initial compactor of the kit of FIG. 5 , according tosome embodiments.

FIG. 10 shows a final compactor of the kit of FIG. 5 , according to someembodiments.

FIGS. 11-14 are illustrative of a method of implanting and forming thejoint system of FIG. 1 , according to some embodiments.

While the invention is amenable to various modifications, permutations,and alternative forms, specific embodiments have been shown by way ofexample in the drawings and are described in detail below. Theintention, however, is not to limit the invention to the particularembodiments described. On the contrary, the invention is intended tocover all modifications, equivalents, and alternatives falling withinthe scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

FIG. 1 is a schematic view of a joint system 10 (e.g., a glenohumeraljoint system) including an interpositional implant 12, a first boneystructure, or bone (e.g., a humerus H) and a second boney structure, orbone (e.g., a glenoid G), where the first and second boney structuresarticulate about the interpositional implant 12. As shown in FIG. 1 , insome embodiments, the interpositional implant 12 is interposed betweenthe two boney structures—the humerus H and the glenoid G—to help repairjoint function. Although the implant 12 is primarily discussed as beingimplanted in a human patient's shoulder, the implant 12 may also bemodified and implanted in other locations. For example, the implant 12is optionally modified to be implanted between a variety of boneystructures in a hip, ankle, hand, foot, or other joint, for example,whether human or other animal.

Generally, the interpositional implant 12, also described as aninterpositional prosthesis, is formed as a single piece, or monolithicunit, and includes at least two convex surfaces, although implantsformed of separate, connected parts are contemplated. As shown, theimplant 12 includes a convex first surface 18 and a convex secondsurface 20 opposed to the first surface 18, though the interpositionalimplant 12 is optionally non-spherical and the surfaces 18, 20optionally have different radii of curvature from one other. As shown,the first surface 18 is in direct contact with the glenoid G, and inparticular the glenoid cavity, and the second surface 20 is in directcontact with a portion of the humerus H.

The implant 12 generally defines a midline M between the first andsecond convex surfaces 18, 20. For example, while FIG. 1 shows agenerally spherical, or spheroid shape for the interpositional implant12, while FIG. 2 shows an interpositional implant 12A having an upper,spheroid portion above a midline M_(A) and a lower, spherical portionbelow the midline M_(A) having a different radius of curvature. FIG. 3shows an interpositional implant 12B having a more symmetrical spheroidshape (e.g., a prolate spheroid shape) above and below a midline M_(B).In still other embodiments, the convexities of the first and/or secondsurfaces 18, 20 are complex, including multiple radii, including theshapes described in U.S. Patent Application Publication 2007/0225818,filed Mar. 21, 2007, and titled “Non-Spherical Articulating Surfaces inShoulder and Hip Replacement,” the entire contents of which areincorporated herein by reference for all purposes. Moreover, althoughsome shapes for the implant 12 have been described, a variety of shapesare contemplated, such as an egg-shaped implant, for example.

In some embodiments, the interpositional implant 12 defines the midlineM in an antero-posterior plane and a height perpendicular to the midlineM, for example in a supero-inferior plane). In the case of a sphere, thediameter of the sphere corresponds to both the width of the implant 12along the midline M and the maximum effective height of the sphereperpendicular to the midline M. The implant 12 is formed of an outerlayer of pyrocarbon, or pyrolytic carbon, over a graphite substrate oris formed substantially entirely of pyrocarbon, for example. Someexamples of pyrolytic carbon implants and associated use for jointrepair are described in U.S. Pat. No. 6,436,146, filed Jan. 18, 2000,and titled “Implant for Treating Ailments of a Joint or Bone,” theentire contents of which is incorporated herein by reference for allpurposes. In some embodiments, the interpositional implant 12 ischaracterized by a Young's Modulus of from about 10 GPa to about 35 GPa,for example, or from about 21 to about 28 GPa, for example, which isrelatively low compared to the much higher Young's modulus of titaniumimplants. The interpositional implant 12 is optionally hollow orotherwise defines an internal void V as indicated in FIG. 1 by a brokencircle. Although a single, substantially spherical void, or internalhollow portion, is indicated the void V optionally takes a variety ofshapes and forms, including multiple voids (e.g., a plurality of largervoids or a plurality of smaller voids similar to a sponge structure) orother forms. By including one or more voids, the weight of the implant12 is optionally reduced and/or other properties of the implant 12 areadjusted as desired.

As shown in FIG. 1 , the humeral head of the humerus H is removed, orresected, proximate the anatomical neck AN, where the humerus H definesa proximal humerus PH. The humerus defines a recess 22 that issubstantially concave in shape, extending at least through a fullhemispherical arc, although other shapes are also contemplated. Therecess 22, also described as a concavity or a pocket, has anarticulation surface 24, or reinforcement bed, that lines the recess 22which, as described in greater detail below, is optionally formed viacompacting and/or reaming methodology. The articulation surface 24 formsa reinforced bed, or liner, for contacting the interpositional implant12. As described in greater detail, the recess 22 is formed intoepiphyseal/metaphyseal bone of the humerus H and optionally extends intothe diaphysis in some embodiments, though typically preferential tolimit the recess 22 to the metaphyseal bone. Where the recess 22 extendsinto the diaphysis, or where the metaphyseal bone is thin or hasdegenerated, a plug or plugs (e.g., made of bone from the humeral head(not shown) or other bone material) are optionally used to reinforce anyholes or weak spots in the articulation surface 24 produced duringformation. In some embodiments, and as described in greater detailbelow, the articulation surface 24 is formed of cortical orcortical-like bone C that forms over time following surgical insertionof the interpositional implant 12. Generally, the depth of the recess 22is measured or otherwise evaluated from the bottom of the recess 22 to aplane of the resected end of the humerus H, although other referenceplanes are employed as appropriate.

Generally, the interpositional implant 12 is not cemented, adhered, orotherwise fixed to the articulation surface 24, leaving theinterpositional implant 12 free to rotate in the recess 22. In someembodiments, however, there is some frictional engagement between therecess and the interpositional implant 12—for example, in associationwith press fitting the interpositional implant 12 into the recess 22and/or following growth of the humerus H.

The glenoid G defines an articulation surface 28 and, in someembodiments, the articulation surface 28 corresponds to the naturalglenoid cavity where no or very little surface modification is made tothe glenoid cavity during implantation. Use of the implant 12 with anunmodified glenoid cavity can be particularly beneficial for partialreplacement of a shoulder joint in cases where the rotator cuff is stillfunctional. In other embodiments, the articulation surface 28 is formedinto the scapula S at the glenoid cavity (e.g., using the reaming and/orcompacting methodology similar to that used with the humerus H(described in greater detail below) or a glenoid component is attachedto the glenoid G for interacting with the implant 12 as shown in FIG. 4.

As shown in FIG. 1 , and as discussed in greater detail below, theinterpositional implant 12 optionally interacts directly with anarticulation surface 28 of the glenoid G, e.g., without any intermediatecomponents between the interpositional implant 12 and the glenoidcavity. In some embodiments, and as shown in FIG. 1 , theinterpositional implant 12 also interacts directly with the articulationsurface 24, which is formed in the humerus H according to some methodsof preparing the humerus H for receiving the interpositional implant 12.

In other embodiments, and as shown in FIG. 4 , a joint system 10Afurther includes one or both of a glenoid component 30 (e.g., implantedin a scapula S of the glenoid G) and/or a humeral component 32, such asthose described in U.S. Patent Application Publication 2009/0287309(“the '309 Publication”), filed Dec. 17, 2008, and titled“Intra-Articular Joint Replacement,” the entire contents of which isincorporated herein by reference for all purposes.

The glenoid component 30 includes an articular member 36 with agenerally concave articular surface 38 that engages interpositionalimplant 12A, where the interpositional implant 12A is optionallysubstantially similar to the implant 12 and is laterally remote from theresected surface of the glenoid G in the sense that, if the articularmember 36 were omitted, the interpositional implant 12A would bedirectly juxtaposed with the glenoid G (e.g., as is shown in the system10 of FIG. 1 ).

The humeral component 32 optionally supplements, or reinforces, a recess22A in the humerus H, where the recess 22A defines articulation surface24A substantially similar to articulation surface 24. The humeralcomponent 32 optionally includes an articular member 40 with a generallyconcave surface 42 formed from a resected portion of the humerus H andinstalled in the recess 22A according to similar methodology to thatdescribed in the '309 Publication, for example. Where both the glenoidand humeral components 30, 32 are present, the interpositional implant12A is positioned between the articular member 36 of the glenoidcomponent 30 and the articular member 40 of the humeral component16A—the radius of the interpositional implant 12A being typically equalto or less than the radii of the concave articular surfaces 38, 42.

FIG. 5 illustrates a surgical kit 50, or kit of parts, used inassociation with some surgical methods for implanting theinterpositional implant 12. The kit 50 includes a plurality of reamers60, a plurality of test implants 62, and a plurality of compactors 64.The kit 50 also optionally includes wrenches, pilot hole tips/bits,cleaning tips/bits, and other components as desired. In someembodiments, the kit 50 is prepackaged as a sterile unit and/or isadapted to be sterilized prior to use (e.g., via autoclave).

In some embodiments, the plurality of reamers 60 are described asforming or shaping tools and are provided in graduating sizes. Theplurality of reamers 60 are generally indicated for use in preparing therecess 22 in the resected end of the humerus H. Each of the plurality ofreamers includes a shaft 70 and a cutting head 72. In some embodiments,one of the plurality of reamers 60 is a starter reamer 74 having asmaller cutting head diameter than the other reamers 60. The starterreamer 74 is optionally utilized early in the formation process of therecess 22 in order to form initial cuts into the resected head of thehumerus H, for example. In some embodiments, the starter reamer 74 iscannulated and includes an optional pilot tip (not shown), such as asharp thin projection inserted into the cannulated reamer and projectingfrom the reamer tip to guide the reaming process. The reamers 60 areoptionally adapted to have reaming diameters graduating in size fromabout 34 mm to about 46 mm (e.g., in 2 mm increments), although avariety of dimensions are contemplated.

Each shaft 70 is optionally color coded and/or otherwise marked withindicia (e.g., lettering) which, as described in greater detail,indicates whether a particular reamer 60 belongs to a correspondingoperational tool set, where the tool sets are generally grouped by size(e.g., corresponding to an expected size for the implant 12 to be placedin the resected head of the humerus H). The cutting head 72 of one ofthe plurality of reamers 60 is shown in FIG. 6 , according to someembodiments. Each of the reamers 60 is optionally substantially similarother than differing generally in reaming diameter, and as such thecutting heads of the plurality of reamers 60 are described collectivelywith reference to the head 72 shown in FIG. 6 .

As shown in FIG. 6 , the head 72 is generally dome-shaped and includes aplurality of arcuate blades 76, the profiles of which define a cuttingor forming surface. In particular, the head 72 has a substantiallyconvex outer profile such that the head 72 is adapted to cut, or carve agenerally concave recess into bone, e.g., into the resected head of thehumerus H. The convex outer profile of the cutting head 72 extends atleast through a full hemispherical arc that defines a reaming diameterof the cutting head 72. In some embodiments, the head 72 is adapted tocut at least a full hemisphere and optionally includes an extendedcutting portion 78 sweeping upward beyond a hemispherical cuttingportion 79 of the cutting head 72. By extending the diameter of cut to afull hemisphere or more, the head 72 is adapted to form fullyhemispherical recesses and recesses deeper than the diameter of cut ofthe cutting head 72. In some embodiments, the extended cutting portion78 includes one or more demarcation lines RL for indicating one or moreselected reaming depths (two are shown in FIG. 6 , though more or lessare employed as appropriate). In some embodiments, a first one of thedemarcation lines RL is located approximately at a height correspondingto the transition from the hemispherical cutting portion 79 to theextended cutting portion 78 and a second one of the demarcation lines RLis located a pre-determined height above the first demarcation line RL,although a variety of heights are contemplated. As shown, thedemarcation lines RL are optionally grooves formed into the blades 76that are adapted or otherwise configured to be viewed by a surgeonduring reaming.

FIG. 7 shows a first test implant 62A of the plurality of test implants62 along with an associated handle 80 for manipulating the test implants62. In some embodiments, each of the test implants 62 is substantiallysimilar other than differing generally in size and color, and as suchthe test implants 62 are described collectively with reference to thefirst test implant 62A shown in FIG. 7 . Though the test implants 62 areshown as being substantially similar, it should be understood that testimplants of differing shape, material, or other characteristic(s) arealso contemplated.

As shown, the first test implant 62A is substantially spherical, orspheroid, and has one or more test depth lines DL. In some embodiments,a first one of the test depth lines DL is located approximately at aheight corresponding to an equator of the first test implant 62A and asecond one of the test depth lines DL is located a pre-determined heightabove the first test depth line DL, although a variety of heights arecontemplated. Although two test depth lines DL are shown in FIG. 7 , agreater or fewer number are contemplated as appropriate. As referencedabove, the first test implant 62A is optionally color coded and is madeof a material that is suitable for being temporarily implanted to checkwhether the implant 12 will perform as desired. The first test implant62A also includes a receptacle 82 for securing the first test implant62A to the handle 80. For example, the receptacle 82 optionally includesfemale threads for mating with the handle 80. In some embodiments, thetest implants 62 having diameters graduating in size similar to the sizeselections available for the implant 12, for example from about 36 mm toabout 46 mm (e.g., in 2 mm increments), although a variety of dimensionsare contemplated.

As shown, the handle 80 includes an elongate shaft 84 terminating with atip 86 suitable for connecting to the test implants 62. For example, thetip 86 is optionally provided with male threads for securing the tip 86to receptacles in the test implants 62, such as the receptacle 82 in thefirst test implant 62A.

In some embodiments, the plurality of compactors 64 are described asforming or shaping tools and are provided in graduating sizes. Thoughgenerally used to form a compacted, more structurally sound surface, thecompactors 64 are also optionally used to break up and remove pieces ofbone as appropriate. In some embodiments, the plurality of compactors 64include a starter compactor 90 (FIG. 8 ) with an optional pilot tip, aplurality of initial compactors 92 (such as the one shown in FIG. 9 ),and a plurality of final compactors 94 (such as the one shown in FIG. 10). As described further, and according to some methods, the startercompactor 90 is optionally used to begin the compacting process, one ormore of the initial compactor 92 are used to continue the compactingprocess, and one of the final compactors 94 is used to finalize therecess 22 into a suitable depth and form for receiving the implant 12.

The starter compactor 90 shown in FIG. 8 has a convex compacting surface100, also described as a forming surface, that extends through ahemispherical arc and is adapted to break up and compact bone (e.g.,cancellous or spongy bone) as it forms a substantially concave cavity.As shown, the convex compacting surface 100 is generally equal to a fullhemisphere in shape as designated by the broken line in FIG. 8 ,although the compacting surface 100 is optionally extended beyond a fullhemispherical shape. For example, in some embodiments the compactingsurface 100 is continued to sweep beyond a hemispherical shape. Asshown, the starter compactor 90 optionally includes a pilot tip 102 tohelp ensure an accurate starting point for forming the recess 22. Insome embodiments, the starter compactor 90 is adapted to have aforming/compacting diameter of about 20 mm, although a variety ofdimensions are contemplated.

The initial compactors 92 graduate in size and, through an iterativeprocess, can be used to progressively form a larger and larger compactedrecess into the resected end of the humerus H. The initial compactors 92are optionally substantially similar other than differing generally insize, and as such the initial compactors 92 are described collectivelywith reference to a first initial compactor 92A shown in FIG. 9 . Insome embodiments, the initial compactors 92 are adapted to haveforming/compacting diameters graduating in size from about 22 mm toabout 34 mm (e.g., in 2 mm increments), although a variety of dimensionsare contemplated.

The first initial compactor 92A has a compacting surface 110 adapted tobreak up and compact bone (e.g., cancellous or spongy bone) as it formsa substantially concave cavity with the compacting surface 110.Similarly to the starter compactor 90, the convex compacting surface 110is equal to a full hemisphere in shape, although other configurationsare contemplated. For example, in some embodiments the compactingsurface 100 is continued and sweeps beyond the fully hemisphericalshape.

The final compactors 94 also graduate in size and are each optionallycolor coded to a corresponding one of the reamers 60 and test implants62 forming one of the operational sets. For example, as shown in FIG. 5, each of the final compactors 94 includes indicia I, such as a coloreddot, for indicating to which operational set the compactor 94 belongs.The final compactors 94 are optionally substantially similar other thandiffering generally in size, and as such the final compactors 94 aredescribed collectively with reference to a first final compactor 94Ashown in FIG. 10 . In some embodiments, the final compactors 92 areadapted to have forming/compacting diameters graduating in size fromabout 36 mm to about 46 mm (e.g., in 2 mm increments), although avariety of dimensions are contemplated.

The first final compactor 94A has a compacting surface 120 adapted tobreak up and compact bone (e.g., cancellous or spongy bone) as it formsa substantially concave cavity with the compacting surface 120. As shownin FIG. 10 , the compacting surface 120 defines a hemispherical portion122 and an upswept portion 124, where the compacting surface isextended, sweeping upward along a substantially straight line beyond thehemispherical portion 122 through the upswept portion 124. In at leastthis manner, the compacting surface 120 is adapted to form/compact therecess 22 to a full hemisphere and to a depth greater than theforming/compacting diameter while helping ensure that substantially all,or at least a greater portion of, the articulation surface 24 iscompacted and thereby reinforced for receiving the implant 12.

In some embodiments, the first final compactor 94A defines one or morevisible demarcation lines CL (e.g., a groove or line in the compactingsurface 120) at one or more predetermined heights from the bottom of thecompacting surface 120 for delineating a desired forming/compactingdepth at which to cease a compacting process. Although two demarcationlines CL are shown in FIG. 10 , embodiments with greater or fewerdemarcation lines are contemplated as appropriate. In some embodiments,the demarcation lines CL are provided in regular increments (e.g., 2 mm)for indicating a plurality of formation/compaction depths. In someembodiments, a first one of the demarcation lines CL is locatedapproximately at a height corresponding to the transition from thehemispherical portion 122 to the upswept cutting portion 124 and asecond one of the demarcation lines CL is located a pre-determinedheight above the first demarcation line CL, although a variety ofheights are contemplated. Moreover, in some embodiments the demarcationlines RL, the test depth lines DL, and/or the demarcation lines CL areprovided at corresponding heights to one another, such that a singleoperational set (described in further detail below) has a uniform set ofdepth markings on the tool used in a surgical joint repair/replacementprocedure to form the recess 22 to a demarcated depth using the markingson the compactors 60 and reamers 64 and test the performance of therecess 22 to that depth using the markings on the test implant 62.

As referenced above, in some embodiments the reamers 60, test implants62, and final compactors 94 graduate in size and are color coded and/orinclude indicia (e.g., writing) to group reamers 60, test implants 62,and compactors 64 into operational sets. For example, a singleoperational set is optionally designated by a single color, where thesingle operational set includes one of the reamers 60, one of the testimplants 62, and one of the compactors 64. Table 1 that follows isprovided as an illustrative example and shows diametricalreaming/forming/test dimensions corresponding to a plurality ofgraduating, color coded operational sets, according to some embodiments,although other dimensions, color coding, and/or other indicia arecontemplated.

TABLE 1 Operational Sets Compactor Reamer Test Implant Operational SetDiameter Coding Coding Coding 1 36 mm Red Red Red 2 38 mm Yellow YellowYellow 3 40 mm Green Green Green 4 42 mm Blue Blue Blue 5 44 mm GreyGrey Grey 6 46 mm White White White

In view of the foregoing, a surgeon or other user provided with thesurgical kit 50 is able to quickly and reliably select an operationaltool set for a particular implant size.

Some methods for implanting the interpositional implant 12 to form thejoint system 10 are described below with reference to FIGS. 1-10(previously discussed) and FIGS. 11-14 which are illustrative of amethod of selecting an appropriate depth of implantation.

In some embodiments, a preoperative assessment of the existing (e.g.,degenerated) joint system in the patient is performed. The preoperativeassessment optionally includes using frontal and axillary radiographs,as well as CT scanning to evaluate orientation of the glenoid G, qualityof bone stock in the humerus H and glenoid G, and any muscledegeneration of the rotator cuff, for example. Based upon thepreoperative assessment, the surgeon makes an initial determination ofthe optimal size and/or shape of the implant 12. In some embodiments,the implant 12 is available in a variety of diameters, where the surgeonor other user initially selects from a plurality of sizes (e.g., such as36 mm, 38 mm, 40 mm, 42 mm, 44 mm, and 46 mm diameter spheres, althougha variety of dimensions are contemplated). From the foregoing, in someembodiments, each of the sizes has a corresponding operational set to beused during implantation, such as those shown in Table 1.

Exposure of the humerus H and glenoid G is optionally accomplished viaany of a variety of techniques. In some embodiments, the surgicalincision is made using a deltopectoral approach to the humerus H andglenoid G. The incision is made from a tip of the coracoid process andfollows the deltopectoral groove. The upper part of the pectoralis majoris optionally released to improve external rotation, the clavipectoralfascia is incised at an outer edge of the coracobiceps, and theacromioclavicular ligament is partially severed to facilitate exposureof the sub-scapular and circumflex vessels. The circumflex vessels arethen ligated to achieve hemostasis during the entire surgical procedure.The axillary nerve is identified and protected. After the superiorarthrotomy, the subscapularis is incised with the capsule to about aninch and a half of the bicipital groove at the neck anatomy. By raisingthe arm in adduction and external rotation and retropulsion, the humeralhead is then dislocated forward. The anterior capsule is released fromfront to back, allowing the exposure of osteophytes. Ultimately, thehumeral head is freed and displaced from the glenoid G and exposed forprocessing.

As indicated in FIG. 11 , once dislocated, the humeral head HH isresected (e.g., at the anatomical neck AN) to form a resected enddefining a resection plane O (FIG. 12 ). Transverse dimensions of theanatomical neck AN or the resected humeral head are then measured usingcalipers or other measuring tool in at least two planes to assess thesize of implant use. In some embodiments, the two planes are generallyperpendicular to one another, such as the antero-posterior andsuperoinferior planes. In some embodiments, where the measurements alongthe planes are different from one another, the smallest of themeasurements is selected as the humeral head size. In some embodiments,the implant size is either initially selected or is confirmed to beabout 2 mm to about 4 mm below the humeral head size.

In order to determine a depth at which the implant 12 is to be installed(or alternatively, to what depth the recess 22 should be formed), thesmallest of the resected end measurements is selected as the initialresected end diameter D.

As shown in FIG. 12 , based upon empirical or other data, the resectedend diameter D is correlated to a predicted projection height A, alsodescribed as a desired projection height A, of the implant 12 above theresection plane O that will help ensure proper tensioning of theglenohumeral joint once the implant is received by the glenoid G and thejoint has healed. For example, empirical data may be obtained relatingto natural projection heights (i.e., in healthy joints) of the humeralhead relative to humeral head diameter at the anatomical neck. Athickness of the cortical bone at the resection plane O is eitherestimated via empirical data or is directly measured using any of avariety of techniques (e.g., using a micrometer, radiographs, andothers). In some embodiments, the implant diameter (and, thereforeimplant radius B) is selected by subtracting the thickness T of thecortical bone from the end diameter D (D−(2×T)=implant diameter). Asshown in FIGS. 12 and 13 , generally, the radius B of the implant 12 isgreater than the predicted projection height A, such that B minus Aequals the depth the midline M of the implant 12 is preferably pusheddown with respect to the resection plane O in order to help ensure thesurface of the implant 12 projecting from the recess 22 iswell-positioned for proper tensioning of the joint as shown in FIG. 14 .In terms of implant height, the depth the midline M is depressed withrespect to the resection plane O is one-half the implant height minusthe predicted projection height A.

In some embodiments, after a diameter of the implant 12 is selected andthe depth of the recess 22 is determined, the recess 22 is formedaccording to a reaming and compacting process. With the implant diameterknown, the surgeon selects the corresponding operational set (one of thereamers 60, one of the test implants 62, and one of the compactors 64)for forming the recess 22.

The reaming and compacting processes are generally used iteratively toform the recess 22 with an adequate depth. As previously referenced, thereamers 60 are well suited to forming a fully hemispherical and/ordeeper shape for the recess 22 (in comparison to traditional reamersthat terminate the cutting surface prior to a full hemisphere).

Similarly, the compactors 64 are also well suited to forming fullyhemispherical recesses and/or deeper recesses. In some embodiments, thevisible demarcation on each of the final compactors 94 (e.g., visibledemarcation CL) corresponds to the desired depth to which the recess isto be formed and compacted relative to the resection plane O, which, insome embodiments is greater than the radius B of the implant 12 by anamount corresponding to the implant radius B minus the predictedprojection height A. Using the visible demarcations, such as demarcationCL, a surgeon performing the compacting process is readily able tovisualize when the desired recess depth has been achieved.

The compacting process is particularly useful to reinforce thearticulation surface 24. For example, compacting helps artificiallydensify the spongious metaphyseal bone, building a stronger lining orfloor to receive the implant 12. It has been surprisingly found that byusing a relatively low Young's modulus for the implant 12 (e.g., lowrelative to titanium, for example), further bone densification of thearticulation surface 24 is encouraged over time during operationalloading, but without overly stressing the articulation surface 24.Eventually, the bone density at the surface 24 may approach that of thecortical bone of the humerus, as generally indicated in FIG. 14 by thecontinuous, white region on the exterior surface and recess 22 of thehumerus H.

In some embodiments, compaction begins with the starter compactor 90(e.g., being of 20 mm diameter). The starter compactor 90 helpsinitially center the recess 22 in the middle of the resection plane Oand ensures that the recess 22 remains centered during ensuingcompacting/reaming with larger diameter tools.

Compaction of the metaphyseal bone continues by gradually increasing thediameter of compaction with the initial compactors 92 until one of thefinal compactors 94 corresponding to the operational set that has beenselected is used to form the recess 22 to its final, predetermined size.The starter compactor 90 and initial compactors 92 are generally onlyinserted to the depth of their respective compacting surfaces (e.g.,only up to a single radial depth of cut) to help ensure that the recess22 is not initially formed too deep. Thus, in some embodiments, each ofthe starter and initial compactors 90, 92 is inserted to the end of thecutting surface, which marks the height corresponding to a hemisphere.In some embodiments, this also helps avoid risk of humeral fractureduring the initial compacting phases.

Once the recess 22 is sufficiently formed, the final compactor 94 of theselected operational set is used to form the recess 22 to thepredetermined depth by compacting the articulation surface 24 with thefinal compactor 94 until the demarcation line is generally parallel withthe resection plane O. If, during the process, it appears that the finalcompactor 94 will contact the external cortical bone, or if the finalcompactor 94 actually begins to contact the cortical bone, the surgeonoptionally switches to a smaller diameter for the implant 12.

Additionally, where the quality of the metaphyseal bone is poor, thesurgeon optionally strengthens the articulation surface 24 duringcompaction by packing pieces of bone grafts taken from the humeral headinto the recess 22. Depending on the quality of the bone in the humerusH, the compacting and reaming process can lead to an opening on themedullary canal at the bottom of the newly-created articulation surface24. In some embodiments, the surgeon blocks or plugs such an openingwith a plug material (e.g., a cement or bone slurry) or using a plugbuilt using the resected head (e.g., similar to the articular member 36of the joint system 10A shown in FIG. 4 ).

Alternatively, if the cancellous bone is dense and inhibits satisfactorypreparation of the recess 22, the reamers 60 are used to mill/ream therecess 22, where reaming stops once the reamer 60 has been inserted tothe full hemispherical depth of the cutting surface of the reamer 60.Where reaming is needed, the recess 22 is prepared by starting with asmaller reamer diameter (e.g., 34 mm) and gradually increasing thereamer diameter up to the selected diameter of the implant 12. Aspreviously mentioned, reaming and compaction are optionally usedinterchangeably by the surgeon until a satisfactory depth for the recess22 is achieved and the articulation surface 24 is in an acceptablestate.

Once the recess 22 has been formed as desired, the test implant 62 ofthe selected operational set is selected. For example, using the colorcoding previously mentioned, the test implant 62 of the same color asthe final reamer 60 and final compactor 64 is used. The test implant 62is assembled onto the handle 80. The test implant 62 is then introducedin the recess 22. The test depth lines DL of the test implant 62 helpthe surgeon visualize whether the test implant 62 has been sufficientlyinserted into the recess 22 and, in turn, whether the recess 22 isformed to a sufficient depth. The test implant 62 is then placed intocontact with the glenoid G to allow articulation about the test implant62. Stability and mobility testing is performed by physicallymanipulating the humerus. During testing the handle 80 is optionallyremoved to facilitate freedom of movement and later resecured to thetest implant 62 for removal thereof from the recess 22. During thestability and mobility testing, the surgeon verifies there is nogleno-humeral impingement or impingement between the humerus and theacromion.

The test implant 62 is removed after testing with the aid of the handle80. If the surgeon perceives too much tension in the muscles orarticulation of the joint appears particularly tight, a smaller testimplant 62 is and/or a smaller size of the implant 12 is selected or thesurgeon optionally attempts to depress the test implant 62 further intothe recess 22 and/or depress the implant 12 further into the recess uponimplantation thereof. If the surgeon perceives insufficient tension inthe muscles and/or in the case of gleno-humeral impingement, a largersize for the test implant 62 and/or implant 12 can be selected instead,with additional compacting/reaming steps as appropriate.

Once the testing is completed to the surgeon's satisfaction, the implant12 of the selected size (typically of the same diameter as the testimplant 62) is then selected and introduced into the recess 22. In someembodiments, where the implant 12 is formed of pyrocarbon, for example,it is important that the surface of the implant 12 not be marred orotherwise damaged. For example, the implant 12 should not be impactedinto place in the recess 22. The implant 12 is not cemented or otherwisefixed in the recess 22 according to some embodiments. The joint isreformed with the implant 12 in place, for example, according to thegeneral methodology that follows.

The scapula S is repaired tendon-by-tendon as necessary and the aid ofbone sutures secured to the humerus are used as needed. Where fixed tothe humerus, the tendon is optionally displaced medially to promoterecoupration and external rotation. Wound closure proceeds step-by-stepin a traditional manner and the arm can be immobilized with a sling, forexample. Generally, the same post operatives are recommended to that ofa total prosthesis joint replacement (e.g., non-strenuous exercise andwork resumed the first day after surgery with a sufficient waitingperiod before increased stretching/movement of the joint).

Various modifications, permutations, and additions can be made to theexemplary embodiments and aspects of the embodiments discussed withoutdeparting from the scope of the present invention. For example, whilethe embodiments describe concave articular surface above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the features. Accordingly, the scope of thepresent invention is intended to embrace all such alternatives,modifications, permutations, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

The following is claimed:
 1. A bone recess forming tool comprising: aforming head comprising a leading tip and a plurality of arcuate bladeshaving profiles that define a cutting or forming surface; the formingsurface having a convex outer profile such that the forming surface isadapted to form a recess into a bone, wherein the forming surfaceextends through at least a full hemispherical dome and includes anextended cutting portion sweeping upward beyond the full hemisphericaldome; and a demarcation line provided in the extended cutting portion,wherein the demarcation line is visibly distinct from adjacent portionsof the forming surface, wherein the demarcation line is positioned at orabove a transition between the full hemispherical dome and the extendedcutting portion, wherein each of the plurality of arcuate bladessubstantially extend from the leading tip of the forming head to thedemarcation line.
 2. The forming tool of claim 1, wherein thedemarcation line is a groove formed into the forming surface.
 3. Theforming tool of claim 1, wherein the demarcation line is located at aheight corresponding to the transition between the full hemisphericaldome and the extended cutting portion.
 4. The forming tool of claim 3,further comprising a second demarcation line located above thedemarcation line.
 5. The forming tool of claim 4, wherein thedemarcation line and the second demarcation line are grooves formed intothe forming surface.
 6. The forming tool of claim 1, wherein the formingtool is a reamer.
 7. The forming tool of claim 1, wherein the formingtool comprises a cannulated shaft.
 8. A surgical kit of parts forimplanting one of a plurality of joint prostheses, each joint prosthesishaving a different diameter, the kit comprising: a plurality ofdifferent sized test prostheses, each test prosthesis having a diametercorresponding to the diameter of one of the joint prostheses; and aplurality of the forming tool of claim 1, each of the plurality offorming tools being of different size, and each forming tool having adiameter corresponding to the diameter of one of the joint prostheses.9. The surgical kit of claim 8, wherein corresponding test prosthesesand forming tools include colored indicia indicating the operationaltool set to which a particular test prosthesis and a particular formingtool corresponds.
 10. A bone recess forming tool comprising: a forminghead having a forming surface comprising: a convex hemispherical portionthat includes a full hemispherical dome; an upswept portion extendingbeyond the convex hemispherical portion, the upswept portion extendingupward from the full hemispherical dome along a substantially straightline; wherein the forming surface extends through at least the fullhemispherical dome and the upswept portion, and the convex hemisphericalportion of the forming surface is adapted to break up and compact boneas the forming surface forms a substantially concave cavity in the bone;an outer surface extending across the convex hemispherical portion andthe upswept portion without any through-holes; and a demarcation lineprovided in the forming surface, wherein the demarcation line is visiblydistinct from adjacent portions of the forming surface, wherein thedemarcation line is positioned at or above a transition between the fullhemispherical dome and the upswept portion.
 11. The forming tool ofclaim 10, wherein the demarcation line is a groove formed into theforming surface.
 12. The forming tool of claim 10, wherein thedemarcation line is positioned at the transition between the fullhemispherical dome and the upswept portion.
 13. The forming tool ofclaim 12, further comprising a second demarcation line located above thedemarcation line.
 14. The forming tool of claim 13, wherein thedemarcation line and the second demarcation line are grooves formed intothe forming surface.
 15. The forming tool of claim 10, wherein theforming tool is a compactor.
 16. The forming tool of claim 10, whereinthe forming tool is a reamer.
 17. The forming tool of claim 10, whereinthe forming tool comprise a cannulated shaft.
 18. The forming tool ofclaim 17, further comprising a pilot tip extending from the cannulatedshaft.